The present invention relates generally to optical networking, and more particularly, to passive optical networks (PONs) and a method and system for upgrading a conventional PON to a higher performance wavelength-division multiplexed passive optical network (WDM PON) subsequent to the original installation of the conventional PON without disrupting service on the conventional PON.
The development of optical fiber communication technologies has enabled exponential growth in the capacity of backbone networks. PONs have been proposed as a flexible broadband infrastructure for delivering voice, video and data to homes and businesses. The most basic PON architecture consists of an optical transceiver at a central office (CO), connected via an optical fiber to a branching point containing a passive optical splitter located in the vicinity (neighborhood) of the customer, and then connected via multiple distribution fibers to transceivers at or near the homes being served. The PON architecture eliminates the requirement for optical-to-electrical-to-optical (OEO) conversion at each node of the fiber optic network by employing passive optical components such as beam splitters and filters at network nodes instead of active optical components. A PON, therefore, is cost effective when compared to active fiber optic networks, and has significant potential for such “fiber-to-the-home” applications. Although this approach has been proposed and demonstrated in the laboratory for approximately twenty years, the widespread deployment of PONs has only recently begun in the United States.
Over the past several years, the developments of several PON standards have helped pave the way for mass deployments of this technology. The two most important standards processes for PONs are being conducted through the IEEE and ITU-T, respectively. The IEEE effort is focused in the IEEE 803.3ah Ethernet in the First Mile Task Force, which is defining standards for Ethernet PONs (EPON). The ITU-T effort is fed by the Full Service Access Networks (FSAN) organization. This group of service providers and vendors has been responsible for the standardization of ATM PON (APON), Broadband PON (BPON), and Gigabit PON (GPON).
Although these PONs differ in capacity, upstream bandwidth allocation, data encapsulation technology, etc., their underlying passive outside plant (also known as optical distribution network) architectures are very similar.
One feature that has been added to the later generations of ITU-T PON standards (BPON and GPON) has been the ability to broadcast video signals over a separate wavelength band. FIG. 1 is a schematic representation of a GPON including the so-called enhancement band for delivering broadcast video services. As indicated in the FIG. 1, the architecture of a representative GPON includes a CO 100 that comprises a video optical line terminal (OLT) 102 and a data OLT 104 that communicate with a core network. The signals from OLT 102 and OLT 104 are multiplexed at 106. Downstream time-division multiplexed (TDM) data is carried in the optical band from 1480-1500 nm wavelength, upstream time-division multiple access (TDMA) data is carried in the optical band from 1260-1360 nm wavelength, and video is carried in the video enhancement band from 1550-1560 nm wavelength. The EPON bandwidth allocation standard in 802.3ah uses the same 1480-1500 nm wavelength band for downstream communication, while upstream TDMA data is carried in the optical band from 1260-1360 nm wavelength. Techniques to add capacity with additional wavelengths apply to BPON, GPON and EPON. The downstream data is communicated over an optical distribution fiber 108 to a remote node containing an optical power splitter 110 that communicates with a plurality of optical network terminals (in the example shown, ONT1-ONT32) designated by the reference numerals 1121-11232. The wavelength allocation is per ITU-T G.983.3 and for such a GPON with broadcast video in the enhancement band, each ONT 112 contains a triplexer for segregating the three wavelength bands.
FIG. 2 is schematic of a GPON system where the video data is included in the downstream TDM data, thereby obviating the need for a G.983.3 enhancement band. Here, the central office 200 includes a data OLT 204 (no video OLT), that communicates via an optical distribution fiber 208 to a passive optical splitter 210 in a manner similar to that described with respect to FIG. 1. A plurality of optical network terminals (ONT1-ONT32) designated by the reference numerals 2121-21232 are likewise coupled to splitter 210 at the remote node. Considering the large downstream TDM capacity of BPON and GPON (up to 1.2 Gb/s and 2.4 Gb/s, respectively, shared among 32 users), it is possible to distribute video signals using IP packets (IPTV) over the TDM channel. In this expedient, the 1550-1560 nm enhancement band depicted in FIG. 1 is not used.
In view of the expanding use of dedicated “wavelength services,” it would be desirable to provide a way for a service provider to upgrade such fiber distribution networks in a cost effective manner without disrupting service to existing PON users.